You actually managed to get out of memory errors with 16GB ram in X-Plane? I think there should be an achievement award for that I have 8Gb ram, run Skymaxx, HD meshes, textures set to extreme and I still can get 20-40 fps on airbuses/Saab340A But as for the question at hand, I think your CPU is totally fine and should be enough for anything your sim can throw at it. Quick google serach have shown that R9 290 is close competition for geforce 970, so I don't think you should have any issues on that front either. Probably would agree on investing in ram (12Gb is suboptimal, isn't it?). Other than that I think you are pretty set!